1. Field of the Invention
Illustrative embodiments of the present invention relate to a liquid ejection head, an image forming apparatus employing the liquid ejection head, and a method of manufacturing the liquid ejection head.
2. Description of the Background
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional peripherals having several of the foregoing capabilities. Known image forming apparatuses employing a liquid-ejection recording method include inkjet recording apparatuses, which eject liquid droplets from a recording head onto a sheet-like recording medium to form a desired image.
Such inkjet-type image forming apparatuses fall into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets while moving a recording head in a main scan direction, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a recording head fixedly disposed in the image forming apparatus.
Such a recording head (liquid ejection head) may include a pressure generator (actuator) that generates pressure on ink present in a plurality of channels (also referred to as pressure chambers or the like) corresponding to a plurality of nozzle arrays for ejecting ink droplets. Such a pressure generator may, for example, be a piezoelectric actuator including a piezoelectric element, a thermal actuator including a heating resistant, or an electrostatic actuator that generates electrostatic force.
Since the liquid ejection head ejects ink as droplets from the nozzles, the surface properties of a droplet ejection side of a nozzle formation face of a nozzle formation member (nozzle plate) on which the nozzles are formed, that is, a side of the nozzle formation face facing a recording sheet (hereinafter also simply “nozzle formation face”), greatly affects droplet ejection performance. For example, if ink is adhered to a peripheral portion of a nozzle, such adhered ink may cause failures such as an unstable droplet-ejection direction, a reduced nozzle diameter, a reduced droplet-ejection amount (droplet size), and/or an unstable droplet-ejection speed. For these reasons, generally, a liquid-repellent layer (also referred to as a water-repellent layer, an ink-repellent layer, or the like) is formed on the surface of the nozzle formation face to prevent ink from adhering to a nozzle peripheral portion and enhance the droplet ejection performance.
Meanwhile, one known image forming apparatus includes a maintenance-and-recovery mechanism that performs maintaining and recovery operations on a liquid ejection head at a certain timing to prevent nozzle clogging of the head. In the maintenance-and-recovery mechanism, since the nozzle formation face of the liquid ejection head is wiped with a wiper member for cleaning, the liquid ejection head needs a liquid-repellent layer capable of withstanding repeated wiping.
To obtain such durability and liquid repellency, generally, a fluorine-added eutectic plated film or an organic thin film is formed on the liquid-repellent layer, or the liquid-repellent layer is coated with a fluorine or silicone liquid-repellent agent.
For example, in one conventional technique, a plated film is formed by a eutectic reaction of an elliptical hard material and a fluorocarbon polymer. At this time, particles of the hard material protrude from the surface of the liquid-repellent film, enhancing the wiping durability (abrasion resistance) of the liquid-repellent film.
However, such a configuration results in a reduced proportion of a liquid-repellent group in the surface of the liquid-repellent film, causing an increased amount of residual ink to remain on the surface.
In another conventional technique, a thin film layer made of diamond-like carbon (DLC) having good adhesion to the nozzle plate is formed as a part of the liquid-repellent layer on the nozzle formation face of the nozzle plate to prevent peeling of the liquid-repellent layer. Further, a fluoride DLC layer is formed as a part of the liquid-repellent layer to give the nozzle formation face good liquid repellency. In such a configuration, two or more fluoride DLC layers containing different amounts of added fluorine may be formed. In such a case, a smaller amount of fluorine is added to the fluoride DLC layer closer to the DLC layer whereas a greater amount of fluorine is added to the fluoride DLC layer closer to the surface. Thus, the above-described technique attempts to obtain good liquid repellency and the preferred durability capable of maintaining the liquid-repellency by adding relatively large amounts of fluorine.
With the above-described configuration, since the DLC layer has properties similar to those of diamonds, relatively good resistance against scratches caused by wiping of the wiping member may be obtained. However, the DLC layer is relatively easily cracked or peeled by mechanical shock. Further, if there is a difference in coefficient of linear expansion between the liquid-repellent layer and the nozzle plate, for example, when the nozzle plate is bound to a channel member by raising the temperature during manufacture, tensile stress or compression stress may arise between the liquid-repellent layer and the nozzle plate, resulting in bending of the nozzle plate, or peeling or isolation of DLC.
In still another conventional technique, after an ink-repellent fluorocarbon polymer film is formed on the nozzle formation face, the fluorocarbon polymer film is hardened by heating in an inert gas or a vacuum. In such a case, a liquid material in the fluorocarbon polymer film is evaporated by heating, allowing hardening of the fluorocarbon polymer film and formation of a durable ink-repellent film. Further, heating in an inert gas or a vacuum may prevent oxidization of the fluorocarbon polymer film and binding of hydroxyl groups or hydrogen atoms to the fluorocarbon polymer film, allowing formation of an ink-repellent film having good ink repellency. However, such a configuration lacks the necessary durability (i.e., wiping resistance).